Thermal connector for electron tubes and the like



Dec. 26, 1967 w. R. STUART -3,360,033

THERMAL CONNECTOR FOR ELECTRON TUBES AND THE LIKE Filed Dec. 20, 1965 FIG.| 55

' INVENTOR- WILLIAM R. STUART 1 M m% ATTORNEY United States Patent 3,360,033 THERMAL CONNECTOR FOR ELECTRON TUBES AND THE LIKE William R. Stuart, San Carlos, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed Dec. 20, 1965, Ser. No. 515,063 12 Claims. (Cl. 165-47) ABSTRACT OF THE DISCLOSURE A thermal connector comprising a metal block having spaced projections extending from a surface thereof, a beryllium oxide block brazed to the ends of the projections, and means for detachably connecting the connector to a device to be cooled. When such device is an external anode electron tube, the metal block is in the form of a fiat disc which is screwed to a flat end of the anode.

This invention relates to means for conducting heat away from electron tubes and other devices which need to be cooled. More particularly, the invention relates to a cooling connect-or which is detachable from the device to be cooled.

In the past, cooling of devices such as electron tubes has been accomplished by conducting a flow of cooling fluid such as air or water along the surface to be cooled. More recently, it has been proposed that the heat be conducted away by connecting the anode of an electron tube directly to a relatively large heat dissipating member called a heat sink. For example, a large metal support or chassis for electrical equipment forms a good heat sink. The problem of course is that normally the element to be cooled such as the anode of an electron tube must be electrically insulated from the chassis on which it is mounted.

Thus in order for the directly-connected heat sink approach to Work, the cooling path must include a dielectric between the metal member to be cooled such as the anode of an electron tube and the metal heat sink. At the present state of technology beryllium oxide is the best material for providing the dual function of forming electrical insulation and .at the same time being a good thermal conductor.

It is already proposed that beryllium oxide be connected between the anode of an electron tube and a heat sink. However the prior proposals have not been completely satisfactory in all regards. For example, previous proposals required that the beryllium oxide be permanently attached to the electron tube. In addition, previous proposals attached the beryllium oxide thermal conductor to the tube anode on the side thereof. It has been found ac cording to the present invention that substantially increased benefits can be obtained by making a thermal connector which is detachable and which can be connected to the end of an anode rather than to the side.

According, one object of the present invention is to provide a heat flow path through solid members by means of a thermal connector which is detachable from the device to be cooled. This eliminates the cost of attaching the thermal connector to the device prior to sale, and in addition reduces the number of thermal connectors required in connection with expendable devices such as electron tubes. For example, each time an electron tube wears out it is only necessary to obtain a new tube since the thermal connector can be detached from the dead tube and used again with the new tube.

A further object of the invention is to provide a thermal connector which can be attached to the end of the anode Patented Dec. 26, 1967 on an electron tube. This arrangement permits more simplicity and versatility in mounting an electron tube in its associated equipment. In particular, the arrangement of the thermal connector on the end of the anode permits the tube to be used more effectively in a coaxial line circuit because the cylindrical outer conductor of the coaxial line need not be increased in diameter and made more complex in order to accommodate any cooling structure extending from the side of the anode.

Another object of the invention is to provide a detachable thermal connector designed so that its dielectric member will have a minimum thickness, consistent with a required minimum anode to ground capacitance, and con sistent with a minimum required electrical breakdown distance between the anode potential and ground. The reasons for striving for minimum thickness of the dielectric member is twofold; one reason is that a suitable dielectric material, such as beryllium oxide, is very expensive. The other reason is that even beryllium oxide is not as good a conductor as copper so that the most effective heat path is one that has the most copper and least beryllium oxide.

A further object of the invention is to provide a combined electron tube and detachable thennal connector.

Briefly described, a preferred thermal connector made in accordance with the invention comprises a metal block, a beryllium oxide block brazed to the metal block, and means for detachably connecting the metal Iblock side of the thermal connector to the device to be cooled. When the thermal connector is used in combination with an electron tube having a conventional cup-shaped external anode, the metal body is in the form of a flat disc which is screwed to the flat end of the anode.

The various objects and features of advantage of the invention will become more apparent from the following detailed description wherein reference is made to the accompanying drawings in which:

FIGURE 1 is a cross-sectional view through the center of a thermal connector made in accordance with the in- Vention and showing the connector attached to the upper end of the anode of an electron tube, which upper end is also shown in cross section. The lower portion of the tube is conventional and is therefore shown in elevation. Also shown in section in FIGURE 1 is a portion of a heat sink, and means for clamping the thermal connector to the heat sink.

FIGURE 2 is a view taken on the line 22 of FIG- URE 1 to show a plan view of the thermal connector, as viewed from the metal side of the thermal connect-or.

FIGURE 3 is a view taken on the line 3-3 of FIGURE 1 to show the upper surface of the metal member of FIGURE 1, with the beryllium oxide member removed, and

FIGURE 4 is a partial cross-sectional view similar to the upper part of the tube of FIGURE 1 but showing a modified embodiment of the invention.

Referring in more detail to the drawings, FIGURE 1 shows a thermal connector 1 connected to an electron tube 2. The electron tube 2 has a conventional construction except that it does not employ the usual cooling fins, and instead is cooled ,by means of the thermal connector 1 as will be hereinafter explained in more detail. By way of example, the tube shown in FIGURE 1 is a tube of the type known in the electronics industry as a 4CX250B and is manufactured by Eimac, a division of Varian Associates.

The electron tube shown in the drawings comprises an external anode 3 normally made of copper. The anode is in the shape of an inverted cup so that it provides a cylindrical sidewall surface 4 and a flat end surface 5. Inside the anode, the tube comprises the conventional heater coil 6 positioned inside a cathode cylinder 7 which is co ated with an electron emissive material to provide a flow of electrons from the cathode to the anode 3. Interposed between the cathode 7 and the anode are conventional cylindrical cage-like grids 8 and 9, the former being a control grid and the latter being a screen grid. At the end of the tube opposite the anode a plurality of terminal pins 10 are arranged in a circular array in conventional manner, and a conventional terminal and socketing post 11 projects downwardly on the axis of the tube. Insofar as the present invention is concerned, the detailed construction of the tube other than the anode is not important and therefore is not shown in the drawings, in order to direct attention more clearly to the area of invention.

The thermal connector 1 comprises a dielectric member 14 in the form of a block of beryllium oxide. The characteristics which are required of the member 14 are that it be a good electrical insulator and a good thermal conductor. As of the date of the invention, beryllium oxide is by far the best material for providing these two qualities. The beryllium oxide block 14 is brazed to a metal block 15. The purpose of the metal block 15 is to provide a good thermal connection between the beryllium oxide block 14 and the anode 3 in a manner which is disconnectable. Since the metal block 15 must be an excellent thermal conductor it is preferably made of copper. In order to provide a good thermal connection between the beryllium oxide block 14 and the metal block 15, the two blocks are fbrazed together as indicated by the brazing metal layer 16. Since it is not possible to braze directly to the surface of beryllium oxide the beryllium oxide block 14 is first metalized in conventional manner to provide the metalizing layer 17. The metalizing layer 17 need only be a circular portion on the center part of the beryllium oxide member having a diameter equal to the diameter of the end of the metal block 15. It should be understood that the thickness of the brazing layer 16 and the metaliz-ing layer 17 is not in proportion to the other dimensions shown in the drawings since they are so thin that they would not be visible in the drawings if shown at their actual thickness.

Another aspect of the braze connection between the beryllium oxide member 14 and the metal member 15 is that the coefficients of thermal expansion of beryllium oxide and copper are so vastly different that if a beryllium oxide member is brazed directly to a massive copper member such as the block 15 the differential expansion characteristics will result in cracking the beryllium oxide. In order to prevent such cracking the surface of the copper block 15 is provided with a plurality of intersecting slots 20 and 21 which provide a plurality of spaced projections 22. The beryllium oxide member 14 is thus actually brazed to the ends of the projections 22. Thus as the main body of the copper block 15 tends to move relative to the beryllium oxide block 14 due to their different coefficients of expansion, the projections 22 can yield slightly and thus prevent the full force of the copper expansion or contraction from being transmitted to the beryllium oxide member.

In order to provide a detachable connection between the thermal connector 1 and the anode 3, the beryllium oxide block 14 is provided with a plurality of apertures 24 therethrough, one of which is shown in the drawings. The copper block 15 is provided with an equal number of apertures which are coaxial with the apertures 24. The apertures through the metal block 15 are made with a small diameter section 25 adjacent the anode and a larger diameter section 26 adjacent the beryllium oxide block. The anode 3 is likewise provided with a plurality of apertures 27 which are arranged in the end surface of the anode to match the location of the apertures through the thermal connector 1. The apertures 27 in the anode are threaded so that they can engage the threads on three screws 28 which are received in the apertures in the thermal connector 1. It will be noted that the screws 28 are provided with heads 29 which seat on the shoulder between the different diameter portions 25 and 26 of the apertures through the metal block 15. Similarly, it will be noted that the depth of the large diameter portion 26 is suificient that the heads of the screws do not project up into the beryllium oxide member so that the full thickness of the beryllium oxide member will be useful for electrical insulation purposes as will be hereinafter described in more detail.

It will be noted that the flat end 5 of the anode is provided with a conventional tubulation portion 32. In order to accommodate the tubulation 32 the metal disc 15 is provided with a central recess 33. In addition to the previously described thermal connection reason for employing block 15, it will be seen that block 15 also serves the purpose of providing an adaptor to present a properly shaped metal surface to which the dielectric member 14 can be attached. Thus, if the metal member 15 were not em ployed and the same amount of electrical insulation were required of the beryllium oxide member 14 as is shown in FIGURE 1, the beryllium oxide member 14 would have to be increased in thickness to provide both the shape shown for the beryllium oxide member 14 and the copper member 15. This arrangement would present two difficulties: (1) being a matter of cost since the price of beryllium oxide is substantially higher than that of copper. The other disadvantage is that copper is a better thermal conductor than beryllium oxide so that when the length of the thermal path through beryllium oxide rather than copper is increased, the cooling ability of the construction is decreased. Alternatively, if the thickness of the beryllium oxide member 14 were not changed from that shown in the drawing and instead were itself recessed to accommodate the exhaust tubulation 32, there would still be several problems, one problem would be that the shortest distance between the metal of the anode 3 namely, the tip of the tubulation 32 and the metal heat sink against which the face of the beryllium oxide block 14 is 'butted would be substantially less than the total thickness of the beryllium oxide block as is now the case. Further, it is difficult to make a good thermal connection between the metal of the anode and the beryllium oxide block 14 in a manner which is detachable rather than brazed permanently to the anode. Also, if the exhaust tubulation were placed in another position so that the end of the anode were completely flat and even if beryllium oxide could be screwed against the anode surface to provide a sufficiently good thermal junction the problem of decreased insulating distances would still exist because the screw head 29 would then have to be seated inside the beryllium oxide and therefore reduce the insulating path through the beryllium oxide.

As previously stated the free face of the beryllium oxide member 14, which is the upper face as oriented in FIG- UR=E 1 is intended to be held tightly connected to a metal heat sink. By way of example in FIGURE 1, the member 14 is shown connected to a heat sink indicated at 34. The metal heat sink can be merely a large mass of metal such as a part of the equipment in which the tube is associated. The beryllium oxide member could, for best thermal connection, be brazed to the heat sink, in which case the heat sink would require apertures aligned with the apertures 24 so that a screwdriver could reach the screws 23 in order to release the tube. Alternatively the beryllium oxide member can be held against an associated heat sink by means of conventional tow clamps 35 held in place by screws 36 which are threaded into the heat sink. As indicated in FIGURE 2 three such tow clamps is a suitable arrangement. In order to provide a surface on the beryllium oxide member for the tow clamps to engage, the beryllium oxide block 14 is shaped to have a large diameter rim portion 37 and a smaller diameter portion 38 to provide a connecting shoulder 39 for an engagement by the tow clamps. It should be noted that the small diameter portion 38 of the beryllium oxide block is substantially larger in diameter than the adjacent metal block 15. In this way the air gap between the electrical potential of the metal block 15 and that of the tow clamp 35 is no less than the thickness of the beryllium oxide member so that the full thickness of the beryllium oxide member is effective as an electrical insulation path while at the same time providing a relatively short thermal path between the metal member 15 and the heat sink.

FIGURE 4 shows another embodiment of the invention wherein the connection between the thermal connector 1 and the anode 3 is slightly modified. More specifically, in the arrangement shown in FIGURE 4 the anode 3 is provided with a radially outwardly projecting portion 41 adjacent the end surface 5 of the anode. Similarly, the metal block 15' is provided with a radially outwardly projecting portion 42 adjacent its surface which abuts the anode. The portions 41 and 42 are provided with a plurality of coaxially arranged apertures spaced around the circumference of the anode and metal block. The aperture in the projecting portion 42 on the metal block is threaded so that the metal block can be clamped to the anode by means of screws 43 which pass freely through the apertures in the metal projection 41 on the anode and engage the threads in the apertures in the metal projections 42 on the metal block 15'. The outwardly projecting portions 41 and 42 can be in the form of continuous rings or can be individual lugs spaced around the circumference of the anode and metal block 15'.

Although specific details of the present invention are shown and described herein, it is to be understood that modifications may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A thermal connector for electron tubes comprising a metal block, said block having one surface thereof shaped to provide a plurality of spaced projections eX- tendiug outwardly from the metal block, a beryllium oxide block brazed to the ends of said projections, and means for detachably connecting said thermal connector to an electron tube.

2. A thermal connector as claimed in claim 1 in which said metal block has a recess in the center thereof on the side opposite said beryllium oxide block.

3. A thermal connector as claimed in claim 1 in which said beryllium oxide block is in the shape of a fiat disc and has a radially outwardly extending rim thereon adjacent the side opposite said metal block.

4. A thermal connector as claimed in claim 1 in which said metal block has threaded apertures therein on the side thereof opposite said beryllium oxide block and adjacent the periphery of the metal block, and said connecting means comprises screws received in said threaded apertures.

5. A thermal connector as claimed in claim 1 in which said beryllium oxide block has apertures therethrough and said metal block has apertures therethrough in line with the apertures in the beryllium block, and said connecting means comprises screws received in said apertures.

6. A thermal connector as claimed in claim 5 in which said screws have enlarged diameter heads, each of said apertures in the metal block has an enlarged diameter section adjacent the beryllium oxide block, and the length of each of said enlarged diameter sections being at least as long as its respective screw head, whereby said screw heads do not extend into said beryllium oxide block.

7. In combination an electron tube and thermal connector theerfor, said electron tube comprising a cylindrical metal external anode having a fiat end wall, said thermal connector comprising a metal block having a planar surface, a beryllium oxide block brazed to said metal block, and means detachably connecting said planar surface of said metal block to said flat end wall of said external anode.

8. The combination as claimed in claim 7 in which said flat end wall of said external anode has an exhaust tubulation projecting outwardly therefrom, and said metal block has a recess which fits over said exhaust tubulation.

9. The combination as claimed in claim 7, in which said anode is in the form of an inverted cup at one end of the electron tube to provide a cylindrical sidewall and a flat end wall, said anode being provided with threaded apertures opening to said end wall, said metal and beryllium oxide blocks having aligned apertures extending therethrough, and said connecting means comprising screws threaded into said threaded apertures, said screws having enlarged diameter heads, each said aperture through said blocks having a smaller diameter section and a larger diameter section remote from the anode, ad-

jacent said anode said screw heads being received in said large diameter sections, and the diameter of said smaller diameter sections being less than the diameter of said heads.

10. The combination as claimed in claim 9 in which said metal block has a plurality of projections extending outwardly therefrom, and said braze is between said beryllium block and the ends of said projections.

11. The combination as claimed in claim 10 in which said beryllium block has a large diameter portion and a smaller diameter portion, and said smaller diameter portion being adjacent said metal block and larger in diameter than said metal block.

12. The combination as claimed in claim 7 in which said anode has threaded apertures opening to said fiat end wall of said external anode; said metal and beryllium oxide blocks having aligned apertures extending therethrough, and said connecting means comprises screws received in said threaded and said aligned apertures.

References Cited UNITED STATES PATENTS 3,249,680 5/1966 Sheets et al -80 3,261,904 7/1966 Wulc 16580 ROBERT A. OLEARY, Primary Examiner. CHARLES SUKALO, Examiner. 

1. A THERMAL CONNECTOR FOR ELECTRON TUBES COMPRISING A METAL BLOCK, SAID BLOCK HAVING ONE SURFACE THEREOF SHAPED TO PROVIDE A PLURALITY OF SPACED PROJECTIONS EXTENDING OUTWARDLY FROM THE METAL BLOCK, A BERYLLIUM OXIDE BLOCK BRAZED TO THE ENDS OF SAID PROJECTIONS, AND MEANS FOR DETACHABLY CONNECTING SAID THERMAL CONNECTOR TO AN ELECTRON TUBE. 